As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that maybe configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
An information handling system may include multiple transient loads, such as processors and memory, whose power requirements change during operation. A switching regulator, such as a direct current-to-direct current (DC-DC) voltage regulator (VR), may be used to provide power to the transient loads, increasing or decreasing the power output in response to load requirements. A central processing unit (CPU), for example, may operate at a particular voltage, but the power required by the CPU may fluctuate depending on the processing mode (e.g., sleep mode, active mode and boost mode) or the operations to be completed at a given time. When a power increase is required, the VR must increase the output current so that the system processor receives the additional power it requires, while maintaining a substantially constant output voltage. Likewise, when a power decrease is required, the VR must decrease the output current so that the system processor receives less power, while maintaining the output voltage.
A single-phase voltage regulator typically includes a controller, a driver and a power stage for generating and supplying power (e.g., an output current and a voltage) to a load. Some voltage regulators are capable of operating in multiple phases. In multi-phase voltage regulators, a driver stage and a power stage are combined to form one phase, and multiple instances of such phases are coupled in parallel to provide varying ranges of output current. During periods of high loads, the multi-phase voltage regulator may function with all phases in operation. For lighter loads, it may employ phase-shedding and operate with a reduced number of phases.
Each phase in a single-phase or multi-phase voltage regulator typically includes a high-side transistor and a low-side transistor, which are driven by corresponding drivers, and an inductor, which is coupled between the transistors for providing an output current to a load. The amount of output current (or “phase current”) provided by each phase generally depends on the switch state of the high-side and low-side transistors and the inductance of the inductor.
Voltage regulators transfer power from an input source to the load by charging and discharging the inductor(s) in the power stage(s) during each switching cycle. The charging and discharging of the inductor causes an alternating current, referred to as a ripple current, to flow through the inductor(s). Although necessary for the voltage regulator to properly function, the inductor ripple current results in power losses in the inductor and in the switching transistors. During light load conditions (e.g., during a sleep mode or low-power state), the relative ripple current magnitude may be significant, resulting in significant power loss even when the voltage regulator is powering a light load. This is highly undesirable, especially in battery powered systems and devices where battery life is of great concern.
In some cases, the inductor ripple current may be reduced and power conversion efficiency may be improved by increasing the inductance of the inductor(s) in the power stage(s). However, increasing the inductance impairs the regulator's ability to respond to changing loads (i.e., degrades the regulator's transient response) by limiting the speed at which the regulator's output current magnitude can change. On the other hand, transient response may be improved by reducing the inductance of the inductor(s) in the power stage(s) at the expense of reduced power conversion efficiency.
There is a conflict in traditional voltage regulator design, especially with regard to inductor optimization, to meet both stringent transient demand and high efficiency requirements. This conflict is particularly problematic when designing voltage regulators for processors and other information handling resources that present large transient loads to the voltage regulator. In one example, a 165 W CPU configured for operating in turbo boost mode may require a maximum load current (ICC) step up to about 187 A. In order to ensure adequate power delivery at high current loads, the voltage regulator design is forced to use a smaller inductance. Unfortunately, a smaller inductance results in large inductor current ripple in both pulse frequency modulation (PFM) and continuous conduction mode (CCM) operation, which reduces the system power conversion efficiency. Although a larger inductance would improve the power conversion efficiency, it impedes the di/dt current slew rate in load transient scenarios, which creates undesirable voltage excursion and jeopardizes system reliability.
One solution for meeting both transient demand and high efficiency requirements is to include a non-linear or variable inductor (i.e., an inductor whose inductance varies with drive current) in the VR power stage(s). This enables the inductance of the variable inductor to be increased to reduce inductor current ripple during light load conditions, and decreased to increase the current slew rate during load transients. Although various types of non-linear and variable inductors have been used for such purposes, the changing inductance value adversely affects the system stability.